What Is a Black Light?

Black Lights and Ultraviolet Lamps

Ultraviolet light is invisible, but black lights or UV-lamps also emit some visible violet light.
Ultraviolet light is invisible, but black lights or UV-lamps also emit some visible violet light.

tzahiV, Getty Images

Have you ever wondered what a black light is? Did you know there are different types of black lights? Here's a look at what black lights are and how you can find and use a black light.

Key Takeaways: What Is a Black Light?

  • A black light is a type of lamp that emits primarily ultraviolet light and very little visible light. Because the light is outside the range of human vision, it is invisible, so a room illuminated with a black light appears dark.
  • There are many types of black lights, including special fluorescent lamps, LEDs, incandescent lamps, and lasers. These light are not created equal, as each produces a unique spectrum of light.
  • Black lights are used to observe fluorescence, in tanning beds, to attract insects, for artistic effects, for disinfection, and to cure plastics.

What Is a Black Light?

A black light is a lamp that emits ultraviolet light. Black lights also are known as ultraviolet lamps, UV-A light, and Wood's lamp. The name "Wood's lamp" honors Robert Williams Wood, the inventor of glass UV filters. Nearly all of the light of good black light should be in the UV portion of the spectrum, with very little visible light.

Why Is a Black Light Called a "Black" Light?

Although black lights emit light, ultraviolet light is not visible to human eyes, so the light is "black" as far as your eyes are concerned. A light that only gives off ultraviolet light would leave a room in apparent total darkness. Many black lights also emit some violet light. This allows you see that the light is on, which is helpful in avoiding over-exposure to ultraviolet light, which can damage your eyes and skin.

Types of Black Lights

Black lights come in many different forms. There are incandescent lights, fluorescent lamps, light-emitting diodes (LEDs), lasers, and mercury-vapor lamps. Incandescent lights produce very little ultraviolet light, so they actually make poor black lights.

Some consist simply of filters over other light sources that block visible light but permit the passage of ultraviolet wavelength. This type of bulb or filter generally produces light with a dim violet-blue cast, so the lighting industry designates these devices as "BLB," which stands for "blacklight blue."

Other lamps lack a filter. These lamps tend to be brighter in the visible spectrum. A good example is the type of fluorescent bulb used in "bug zappers." This type of lamp is designated "BL," which stands for "black light."

Black light or ultraviolet lasers produce coherent, monochromatic radiation that is completely invisible to the human eye. It's particularly important to wear eye protection when working with such devices because the light can cause immediate and permanent blindness and other tissue damage.

Black Light Uses

Black lights have many uses. Ultraviolet light is used to observe fluorescent dyes, improve the brightness of phosphorescent materials, cure plastics, attract insects, promote melanin production (tanning) in skin, and illuminate artwork. There are multiple medical applications of black lights. Ultraviolet light is used for disinfection; diagnosing fungal infections, bacterial infections, acne, melanoma, ethylene glycol poisoning; and in treatment of neonatal jaundice.

Black Light Safety

Most black lights are relatively safe because the UV light they emit is in the longwave UVA range. This is the region closest to that of visible light. UVA has been linked to human skin cancer, so extended exposure to black light radiation should be avoided. UVA penetrates deeply into skin layers, where it can damage DNA. UVA does not cause sunburn, but it can destroy vitamin A, damage collagen, and promote skin aging.

Some black lights emit more light in the UVB range. These lights can cause skin burns. Because this light has a higher energy than UVA or visible light, it can damage cells more quickly.

Ultraviolet light exposure can damage the lens of the eye, potentially leading to cataract formation.

Sources

  • Gupta, I. K.; Singhi, M. K. (2004). "Wood's Lamp." Indian J Dermatol Venereol Leprol. 70 (2): 131–5.
  • Kitsinelis, Spiros (2012). The Right Light: Matching Technologies to Needs and Applications. CRC Press. p. 108. ISBN 978-1439899311.
  • Le, Tao; Krause, Kendall (2008). First Aid for the Basic Sciences—General Principles. McGraw-Hill Medical.
  • Simpson, Robert S. (2003). Lighting Control: Technology and Applications. Taylor & Francis. p. 125. ISBN 978-0240515663
  • Zaithanzauva Pachuau; Ramesh Chandra Tiwari (2008). "Ultraviolet Light- its Effects and Applications." Science Vision. 8 (4): 128.